The present invention relates to electroluminescent displays. More specifically, but without limitation thereto, the present invention relates to an electroluminescent semiconductor formed in porous silicon-on-sapphire.
For many years, silicon has found extensive applications in military and commercial electronics, but was unsuitable for electro-optic applications because single crystal silicon is not an efficient emitter of light. Electro-optic devices that are formed in other semiconductors include laser diodes, optical links between chips, and high speed communications interfaces for fiberoptic cables. Flat panel displays and other devices might benefit substantially from light emitting diodes formed as elements of integrated circuits.
Recently, promising discoveries have been reported in photoluminescent and electroluminescent devices formed in porous silicon. See, for example, "Optoelectronic Applications of Porous Polycrystalline Silicon" by Kalkhoran, Namavar, and Maruska. Because electroluminescence in porous polycrystalline silicon could only be observed from the substrate opposite the gold electrode, the substrate was made of a transparent material such as glass or quartz. However, these materials are not compatible with standard silicon semiconductor manufacturing processes. Also, the gold electrode has an adverse effect on the carrier lifetime in silicon and is less readily etched than other metals. A need therefore exists for an electroluminescent device that may be made with materials that are compatible with silicon manufacturing processes.